1. Field of the Invention
The present invention relates to substrate processing. More particularly, the invention relates to substrate polishing.
2. Background of the Related Art
In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting and dielectric materials are deposited and removed from a substrate during the fabrication process. Often it is necessary to polish a surface of a substrate to remove high topography, surface defects, scratches or embedded particles. One common polishing process is referred to as chemical mechanical polishing (CMP) and is used to improve the quality and reliability of the electronic devices formed on the substrate.
In one example of a polishing process, a substrate is rotated in a substrate support and contacted against a polishing article under controlled pressure, temperature and rotational speed (velocity) of the polishing article in the presence of a chemical slurry or other fluid medium to remove materials from a substrate surface, such as dielectric or conductive materials. The provision of slurry facilitates higher removal rates of deposited films.
An important goal of CMP is achieving uniform planarity of the substrate surface. Uniform planarity includes the uniform removal of material deposited on the surface of substrates as well as removing non-uniform layers that have been deposited on the substrate. One measure of uniformity is referred to as “with-in-substrate non-uniformity” (WIWNU). With-in-substrate non-uniformity refers to the ability of the CMP apparatus to remove features across the diameter of the substrate regardless of substrate shape and/or topography across its surface. Another measure of uniformity is referred to as “with-in-die non-uniformity” (WIDNU), which refers to the ability of the CMP apparatus to remove features within a die, regardless of size and feature density. Successful CMP also requires achieving an acceptable level of WIWNU and WIDNU for a given substrate as well as repeatability from one substrate to the next.
In addition to uniformity, other process parameters that must be controlled include the removal rate and structural defects. Removal rate refers to the rate at which material is removed from a wafer during polishing and is measured in angstroms per minute. In general, a higher removal rate is preferred in order to increase throughput (i.e., the number of wafers processed per unit time). Structural defects refer to undesirable surface defects on the wafer such as dishing, erosion, peeling and delamination.
The various consumables of CMP (e.g., the polishing article and slurry) each affect the ability to control the processing parameters described above (i.e., uniformity, removal rate and structural defects) of polished substrates. As a result, characteristics of the polishing article and slurry have been extensively studied and controlled in an effort to achieve a desired result. For example, it is known that the sufficiency of slurry (i.e., slurry volume and rate of slurry replenishment) and uniformity of slurry over the substrate surface directly impact the processing parameters. Regions of insufficient or relatively non-uniform slurry are referred to as “starved” regions. In these starved regions, the removal rate may be different than in other regions of the substrate, resulting in non-uniformity of the substrate topography.
To ensure the sufficiency and uniformity of slurry delivery, various polishing article designs have been utilized. Specifically, the polishing surfaces of polishing articles are patterned with grooves to allow for slurry flow therein. Two common groove designs are shown in FIGS. 1 and 2, respectively. FIG. 1 shows a polishing article 100 with plurality of grooves 102 arranged concentrically about a central axis 104 of the polishing article 100. Such grooves are commonly referred to as k-grooves. FIG. 2 shows a polishing article 200 with a plurality of grooves 202 arranged in a crosswise manner, often referred to as XY grooves.
FIG. 3 shows a cross-section of a groove 302 formed in a polishing article 300. The groove 302 may be representative of either of the grooves 102 and 202. In general, the groove 302 is defined by a bottom 306 and a pair of sidewalls 308. The sidewalls are vertically inclined and generally orthogonal to the floor 306 and an upper polishing surface 310. The sidewalls 308 and the upper polishing surface 310 meet to define corners 304.
One problem with conventional grooved polishing articles is that the corners 304 can produce undesirable effects. Specifically, the corners act as a knife edge against the wafer being polished, resulting in delamination and/or peeling of material from the wafer. This phenomenon is illustrated with respect to FIG. 4. FIG. 4 shows the polishing article 300 described above with reference to FIG. 3.
A wafer 400 is shown disposed on the polishing surface 310. During polishing, a downward pressure is applied to the wafer 400 with respect to the polishing article 300, thereby at least partially compressing the polishing article 300. The amount of compression is indicated by a distance D between the compressed polishing surface 310 and the uncompressed polishing surface 310. In addition, the wafer 400 and the polishing article 300 are rotated relative to one another while the wafer 400 is moved laterally over the surface of the polishing article 300, as indicated by the horizontally oriented arrow (indicating velocity). As a result, an edge 402 of the wafer 400 will periodically encounter a corner 304 of an uncompressed portion of the polishing article 310. The resulting contact between the edge 402 and the corners 304 can damage portions of the wafer 400, primarily at the edge 402. The detrimental cutting effected by the corners 304 is particularly severe where XY grooves are used. This is because, in addition to forming sharp or “knife” edges, the intersections of the XY grooves form points, which are particularly destructive to the material disposed on the wafer.
Therefore, there is a need for a polishing article that mitigates damage to wafers.